In a typical fluid treatment purification system utilizing ultraviolet (UV) energy, the fluid, which may be a liquid and/or gaseous substance contaminated by pathogenic organisms is moved through a treatment zone. Typically, the UV energy is provided by causing a discharge in a gaseous medium contained in a UV transmission bulb or envelope. Typical gas fillings include mixtures of argon (and/or other gases such as xenon XE, krypton KR) and mercury which, upon discharge therein, is rich in ultraviolet (other UV rich gases on ionization may be used). Typically, a ballast power supply is connected to the electrodes. In electronic ballast systems, a step-up transformer provides a high striking or ionization voltage, several hundred volts (which, once the lamps are energized, is lowered to a normal operating voltage (normally in the range of 100-200 volts)). When the ultraviolet lamps are used for large scale water purification systems, the lamps, typically a cylindrical ultraviolet ray-emitting lamp and an outer coaxial and substantially coextensive cylindrical UV transparent sleeve, are arranged in banks or arrays in parallel rows. Various structural arrangements are utilized to enable and facilitate the mounting of the banks or arrays of UV lamps in a water-flow conduit for treatment of the water. Typically, the axis of the UV lamps are parallel to the flow direction of the water.
In some systems, the UV source is driven in two or more intensity modes, a low intensity mode when the fluid flow is low and a high intensity mode when the fluid flow is high. Reference is made to the following prior U.S. patents:
______________________________________ Patent No. Issued Inventors ______________________________________ 4,482,809 11/1984 Maarschalkerweerd 4,872,980 10/1989 Maarschalkerweerd 5,023,518 06/1991 Mans et al 5,081,399 01/1992 Jy 5,230,792 07/1993 Sauska et al 5,324,423 06/1994 Markham 5,401,395 03/1995 Markham 5,503,800 04/1996 Free 5,536,395 07/1996 Kuennen et al 5,547,590 08/1996 Szabo 5,611,918 03/1997 Markham 5,698,091 12/1997 Kuennen et al 5,707,594 01/1998 Austin ______________________________________
Sauska et al U.S. Pat. No. 5,230,792 and Markham U.S. Pat. No. 5,611,918 are typical examples of ultraviolet water purification systems with variable intensity controls. In these patents, the intensity of an ultraviolet lamp is controlled by a circuit which is responsive to fluid flow for selectively energizing the lamp to provide variable UV intensity output depending upon fluid flow. In these circuits, a high striking voltage is required to initiate the discharge and produce ultraviolet. In the case of Sauska et al, the circuit arrangement is such that the ultraviolet lamp is always started with a high-current ballast. This is in order to assure the striking of a discharge, and then a low-mode ballast-is used to maintain the UV lamp in the low output stage status.